How to correctly label images for multi-label classification?
You can't label things you don't know.  The goal of labeling is to label the things you want the classifier to learn so that when you run it in inference mode you can discover what is in your data (new data that you didn't use for training, validating, or testing).

It is not a good idea to label small objects like the 'blue water' unless it is important to you to discover these fine details in inference mode.